To insult one's own work or abilities before presenting them as to soften the blow of possible rejection.

Takes the form of "Well, it's not very good, but..." or the like.

Comes from the old southern tradition of playing down one's food cooked for friends or family. "The dough didn't rise how I was hoping..." etc.

Sarah went to the front of the class to give her speech.
"Ok." She said, "but just know I was up late last night and I don't think I'll be very good at the assignment today."
"Please don't southern-biscuit, Sarah." Replied her teacher. "I'm sure you'll do fine."